The disclosure relates to music capos, which are typically clamped on the neck of stringed instruments to change the play length of the strings, thereby altering the sound.
Many kinds of stringed instruments are known, and capos can be used with numerous such instruments. However, for the purposes of the present disclosure, the background will be discussed and the inventive concepts will be described primarily with regards to guitars. Guitars fall into the three main categories of classical, folk, and electric. Due to several factors, capos are generally designed for use on one type of guitar. A capo configured primarily for one type of guitar is commonly less effective if used on other types of guitars. An effective capo presses down on all the strings between two frets, with enough force to change the play length while preventing unwanted vibration (“buzz”), but without excessively clamping so as to stretch any of the strings over the fret, which results in degradation of string and tuning issues.
One challenging design factor is the difference in string diameter (i.e., gauge) as among the thinner, higher pitch strings and the thicker, lower pitch strings. Classical guitar necks are generally flat, whereas the folk and electric guitars typically have a neck that is radiused in the range of about 7 to 20 inches. Different radii affect playability and the radius is a matter of the personal choice of the instrument designer and the type of player he is targeting. However, whether the neck is flat or radiused, a capo with a flat contact strip cannot easily accommodate all of the strings uniformly. Likewise, a capo with a contoured or radiused contact strip would be more effective for one type of guitar having a particular neck radius, but unsatisfactory for other guitars.
These design factors are especially significant for capos to be used on fretted instruments with strings in pairs. Instruments like twelve string guitars and mandolins, for example, have pairs of strings, some in unison and some tuned in octaves. A twelve string guitar has six courses, each with a side-by-side pair of strings. The top two strings are the same in diameter and pitch but the lower four pairs are tuned in octaves and string diameters are significantly different for each octave. A capo thus must be effective not only transversely across the entire neck, but for the pairs of octaves and those tuned in unison as well.
Efforts have been made to provide a capo that is effective for a wide range of guitar types without significant success. U.S. Pat. No. 4,793,234 (Geis) describes a capo having a rigid upper arm and a hydraulic bladder secured to the underside of the upper arm. U.S. Patent Application Publication No. 2016/0247490 (Campling) discloses a rigid upper arm with a rubber outer layer that encapsulates a rigid chamber and a flowable medium on three sides with a resilient spacer element between the fourth side.
It would be useful to have a capo that is effective on a wide range of string instrument and neck types as well as strings on a given instrument that have a broad range of gauges.